patch 9.1.0984: exception handling can be improved

Problem:  exception handling can be improved
Solution: add v:stacktrace and getstacktrace()

closes: #16360

Co-authored-by: Naruhiko Nishino <naru123456789@gmail.com>
Signed-off-by: ichizok <gclient.gaap@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/evalvars.c b/src/evalvars.c
index 038d7ed..f5fef04 100644
--- a/src/evalvars.c
+++ b/src/evalvars.c
@@ -160,7 +160,8 @@
     {VV_NAME("python3_version",	 VAR_NUMBER), NULL, VV_RO},
     {VV_NAME("t_typealias",	 VAR_NUMBER), NULL, VV_RO},
     {VV_NAME("t_enum",		 VAR_NUMBER), NULL, VV_RO},
-    {VV_NAME("t_enumvalue",	 VAR_NUMBER), NULL, VV_RO}
+    {VV_NAME("t_enumvalue",	 VAR_NUMBER), NULL, VV_RO},
+    {VV_NAME("stacktrace",	 VAR_LIST), &t_list_string, VV_RO},
 };
 
 // shorthand